Actually, that's one of my pet bugbears about Storyline, and it is a badly needed 'feature' - the ability to view items within a State as layers - some sort of popup timeline, or a 'micro-timeline' that becomes active once in the Edit States mode would be awesome.
Sometimes, in files I inherit, there are lots of items hidden in the background behind a shape (for whatever reason) and I usually only find out when troubleshooting issues.
This is a very needed, time saving idea. The ability to be able to re-stack layers within a State would be brilliant instead of the guesswork of 'selecting all', deselecting the desired object, sending items to back, just to get to an element that was obscured in the background.